Method for the manufacture of tantalum powder for condenser purposes



1969 G. o NDLIKER ETAL 3,

ANTALUM POWDER F METHOD FOR THE MA ACTURE O NDENS FUR S 6d Ma 29, l

HYDROGENATING ELECTROLYTICALLY OBTAIN ED TANTALUM PURIFYING THERMALLY IN VACUO (OPTIONAL) GRINDING TO POWDER HAVING PARTICLES TRACE-5% 601] 70-95% 5-60 A: TRACE-30% 5 u DE HYDROGENATING Fig.l

United States Patent 7,404/65 U.S. Cl. 317-230 Int. (:1. H01g 9/02 4 'Claims ABSTRACT OF THE DISCLOSURE A new method is provided for manufacturing tantalum powders which are especially valuable for forming sintered anodes for electrolytic capacitors. In the method of this invention electrolytically obtained tantalum is hydrogenated, and the tantalum hydride obtained is ground into a powder containing a trace to 5% of particles of greater than 60 microns in diameter, 70-95% of the particles being 560 microns in diameter, and a trace to 30% of particles being less than 5 microns in diameter. The powder thus obtained is dehydrogenated to provide the tantalum powder of this invention.

It is known to use tantalum as an anode material for electrolytic condensers. However not all tantalum powders are suitable for the manufacture of sintered shapes for such electrolytic condensers. It is furthermore known that certain requirements have to be set as regards granule size, particle shape and purity if optimum results are to be obtained. The particle shape and the size distribution of the powder particles to a large extent determine the capacity achievable with the sintered shape, and the equivalent series resistance. On the other hand the view exists that the performance of condensers as regards current loss, breakdown voltage and long term performance is the better, the purer the starting material, that is to say the tantalum powder, or the sintered shape.

It has now been found that low leakage currents, high breakdown voltages and favourable long term performance are not only determined by chemical purity but evidently also by other properties, as is evident from the fact that powders of similar chemical composition but produced by different methods show different behaviour.

The present invention now relates to a method for the production of a tantalum powder which is suitable for the production of sintered anodes for electrolytic condensers which have high breakdown voltages, and is characterised by hydrogenating electrolytically deposited tantalum powder, optionally after a thermal vacuum purification, grinding it, selecting a powder mixture having a particle size distribution:

Percent:

3,430,108 Patented Feb. 25, 1969 into the electrolytic condensers takes place by measures which are in themselves known.

FIG. 1 is a flow diagram illustrating the process of the present invention.

FIG. 2 is an enlarged cross sectional illustration of a typical sintered anode formed with the tantalum powder of this invention. The number 10 generally denotes the anode, having a lead wire 12, and a sintered tantalum body 14, comprised of the sintered-tantalum powder of this invention.

EXAMPLE 1 (a) Electrolytically deposited tantalum of high purity is first freed of adhering salt bath residues by leaching out in hydrogen peroxide solution. The dendritic material is then hydrogenated in known manner. The hydride is thereafter comminuted by appropriate means, for example in a tantalum-lined ball mill or roller mill. However, an ordinary steel ball mill may also be used provided the iron taken up during the grinding process is subsequently again dissolved out by means of hydrochloric acid. Other usable comminution methods use a vibratory ball mill.

The ground material is sieved through a sieve of mesh size 40,u.. The coarse fraction is again subjected to the comminution operation and is again sieved. If necessary, the grinding and sieving process is repeated further. The material of particle diameter less than 4071 is now dehydrogenated and used for the manufacture of condensers.

(b) Electrolytically deposited tantalum is, after leaching out as in (a), pressed into tablets and fired for 45 minutes at 1950 to 2000 in a vacuum of 10 torr. After cooling, the tablets are hydrogenated and ground as described under (a).

A considerable purification of the material takes place during this sintering.

Characterisation of the powders prepared by the two methods (a) and (b) of Example 1.

Comparison with other types of powders:

Compact particles:

I-According to Method (a). II-According to Method (b). III, IVCarbothermally reduced tantalum, porous particles. VCommercially available tantalum, porous leafletlike structures.

CHEMICAL ANALYSIS OF THE POWDERS parts per million] I II III IV V 3 Y 4 PHYSICAL CHARACTERISATION and II of the invention show a considerably higher breakdown voltage than those prepared with the comparison 1 H m N V powders, and therefore can be formed at higher voltages. P g m e i y 7 4 6 1 12 6 8 8 6 7 Additionally the loss currents in wet electrolyte are less. g gfg 'agh' iygigggpg'ggffij 5 (2) The anodes manufactured with the powders of the od, g./ir 1ch 102 9 80 93 7O invention can successfully be converted to 50 V. condentfilggfi 0 13 4 14 sers, but the others cannot.

g 2 3g i3 i3 (3) High breakdown voltages and hence high voltage 45 38 29 60 54 ratings in the finished condenser do not only depend on 12 28 8 the purity of the powder but also on its method of manua tur Anodes (dimensions: 5, 6.8 mm.; length, 6.7 mm.) f iyeeclaim:

were pressed from these powders using 2% camphor as a lubricant. The lubricant is driven off in a vacuum furnace and the anodes thereupon sintered for 30 minutes at 15 2070 to 2100 C. The next table gives the dimensional changes and the electrical data on wet testing.

1. A method for producing tantalum powder for sintered anodes in an electrolytic capacitor comprising hydrogenating electrolytically obtained tantalum, grinding the tantalum hydride into a powder containing particles ranging from 5 microns to 60 microns in diameter, selecting a mixture, composed of the hydride particles, with a trace to 5% being greater than 60 microns in diameter,

I II III IV V 70-95% from 5 to 60 microns in diameter and a trace to 30% less than 5 microns in diameter, and dehydrogenating said mixture to form the tantalum powder.

2. The method according to claim 1 wherein the tantalum hydride is purified thermally in vacuo before 1 Measured with tonned anodes m 10% HaPO4 at 0., forming in 25 grinding- Sintered density Shrinkage, percent diameter Resistance 1 2 Loss current, 3 10- ;1./ v Breakdown voltage, v

01312;; {12%)IO4lto 200 v. at 5 3. 2 hours f i g i 3. The method for manufacturing sintered anodes for a M140 a espersecon an electrolytic condensers comprising forming said anodes 4 In H3PO4 at 00 C. Current limit 150 ma-l w from the tantalum powder obtained according to the meth- These anodes were all converted to finished condensers 0d of Claim by the same technique, using Mn0 as the semiconductor 30 0 AH anode for an electl'olym p f 9 P of l t d d were th kept f 250 hours t 85 C sintered tantalum powder having a particle s1ze distribuat their rated voltage. The following table shows the f from 5 microns t0 6O f f, With a trace to resulm belng greater than 60 mlcrons 1n diameter, 70-95% from Long ta m1 beh Mi on r finished condensers 5 to 60 m crons in diameter and a trace to 30% less than Average values of 15 to 20 specimen 5 mlCI'OIlS 1J1 diameter. 250 hours at rated voltage at 85 C.

I III IV V References Cited gatedgoltafge v3 2732 1352 g 333; 333g 26 g apac 2 299 228 10/1942 Gray et al 317-230 Ph 1 c t 40 L1ii 0 c y cl ez:g er econd 14.4 8.6 5.6 9.5 11.2 10.2 2,461,410 2/1949 Clark 317-230 5 c r n OS Bf iiinin? 0.92 0. 63 0. s2 0. 75 1. 0s 1. 0s 3,004,332 10/1961 werfler 317-230 End 0.71 0. 0a 0. 09 1.10 1.20 1.68 3,166,693 1/1965 Hallng et al 317-230 b Tthtilsficsolumn {gives data [or smaller anodes, diameter 3.1 mm., weight 3,302,073 1/1967 Broodo 317 23O a on g.

15?) Forming voltage for v.condensers, 270 v.; for 35 v.condensers, 45 JAMES D KALL AM Primary Examiner v. 3 Cannot be produced.

The data show that: X-R. (1) The condensers manufactured with the powders I -200 

